Thallium-transition-metal bonds

Transition Metal Bond Lengths to Gallium, Indium, and Thallium... 

The discussion of the main group 3-5 and 3-6 compounds in the previous sections was limited to examples in which the group 3 element E is three-coordinate, so that an empty p-orbital on E is available for overlap with a lone pair on the group 5 or 6 atom. For the same reason, the discussion here will focus on those compounds with three-coordination at gallium, indium, or thallium. In the case of the transition metal derivatives, it is transition metal -electrons that are available to overlap with the empty p-orbital on E to form the potential ir-bond, as illustrated in Fig. 26. 

Thallium(I) forms compounds with transition metals, as in T1Co(CO)4, that are mainly salts of carbonylate anions and tend to be ionic. Metal-metal bonds may be cleaved, for example,... 

The transition metal trichalcogenides MX3 (M = Ti, Zr, Hf, Nb, Ta X = S, Se) have been studied in some detail. All the trichalcogenides contain anion-anion bonding and consequently a redox competition exists between electron transfer to the metal center and electron transfer to the anions. The situation is the converse of the deintercalation of the thallium vanadium sulfides, where the competition is between oxidation of T1+ cations and that of the metal sulfur framework. 

Thallium derivatives of transition-metal carbonyls are used to prepare compounds in which Sn is bonded to two different transition metals. Reaction conditions are mild—THF at RT for 0.25 h—and yields are good (80-90%). Reactions with -CpCr(CO)3Tl, which must be carried out in the dark, yield (CO)4CoSnCl2Mn(CO)4(PPh3), > -Cp(CO)3CrSnCl2Mn(CO)4(PPh3), (CO)4CoSnCl2Fe(CO)2Cp- / and i -Cp(CO)3CrSnCl2Fe(CO)2Cp-j/. ... 

The extreme hypoelectronicity of the indium and thallium clusters can be relieved by d-orbital participation from some of the vertex metal atoms. In the case of a normal bare post-transition metal vertex in a metal cluster sucb as those discussed in Section 10.6.1, tbe 12 external electrons may be divided into two types, namely, tbe 10 nonbonding d electrons and tbe 2 electrons of an external lone pair analogous to tbe B-H bonding pair in the polyhedral boranes B H (6 < n < 12). In this way a normal post-transition metal vertex such as indium may be considered to use a four-orbital sp bonding manifold just like light vertex atoms such as boron or carbon. However,... 

The mixture of double bond isomers of l,2,3,4-tetramethyl-5-(trifluoro-methyl)cyclopentadiene (Cp H) is a clear, colorless liquid with a sweet ole-finic odor similar to that of pentamethylcyclopentadiene. Cp H is an air-stable compound but it should be stored in the refrigerator. Although gas chromatographic analysis shows two peaks, the presence of all three of the possible cyclopentadiene isomers is indicated by H NMR spectroscopy as three quartets for the ring protons are observed at 3.26 (Jhf = 10.0 Hz), 2.99 (Jhh = 6.7 Hz), and 2.66 ppm (Jhh = 6.8 Hz) with a relative ratio of approximately 1 16 2.4 for isomers I, II, and III, respectively. Resonances between 4.8 and 5.0 ppm are attributed to products that result from an elimination mechanism rather than cyclization in the last step of the synthesis. These impurities boil very close to that of Cp H, but they are removed by careful fractional vacuum distillation as part of the forerun. The IR spectrum (neat liquid) exhibits significant bands at 2977(vs), 2937(vs), 2884(s), 2864(s), 2751(w), 1658(m), 1599(s), 1446(s), 1384(vs), 1357(vs), 1280(s), 1258(vs), 1164(vs), 1099(vs), 1012(vs), and 686(m) cm . The syntheses of organotransi-tion metal complexes are usually carried out with the 91% purity Cp H product. Because alkali metal and thallium salts of Cp are unstable, organo-transition metal complexes are prepared from Cp H itself, as are many complexes of pentamethylcyclopentadiene and cyclopentadiene."... 

Salt elimination between a transition metal anion and a Group 13 halide is the most extensively exploited route into the formation of transition metal-Group 13 bonds in which the Group 13 element is in the -1-3 oxidation state. Most initial work focused on indium and thallium species and their reactions with mono-anionic carbonylmetaUates. Early examples indude [CpMo(CO)3]3Tl formed via the reaction of TljSO with 3 equiv. of Na[CpMo(CO)3] [202-204]. 

In 1962, Sugano showed that the Seitz model (115) could be interpreted as a molecular orbital model (123), an interpretation that clarifies analysis of these systems. In this interpretation, the absorption bands observed in the TI(I) doped alkali halide system come from the electronic transition aigf a g) hu), but the excited states are still calculated assuming an ionic interaction between the metal and the hgand. Since the thallium-chlorine bond is actually largely covalent, Bramanti et al. (118) modified the approach and used a semiempirical molecular orbital (MO) calculation to describe the energy levels of T1(I) doped KCl. Molecular orbitals were constructed by the linear combination of atomic orbitals (LCAO) method from the 6s and 6p metal orbitals and the 3p chlorine orbitals. Initial calculations were conducted with the one-electron approximation the method was then expanded to include Coulomb and spin-orbit interactions. The results of Bramanti et al. were consistent with experimental... 

---